I have setup a machine manually, installed the desired applications manually and captured that image. This is Windows 7 x64 bit Operating System. Now if a situation raises tomorrow wherein i may need to add more applications, is there a way for me to simply automate this image by injecting some scripts or some methods to install the new application to the existing image without having to rebuild the master image from the scratch?

If so, could you please guide me on how to do that, so that I can test by injecting a new application to the image and try deploying.

Provisioning would be as simple as adding the software distribution packages into your provisioning template under the system configuration

if you are doing OSD, its a little more sophisticated but it can be done. All you would need to do is copy the files you want to install into your image during OSD at the end of your OSD script (or inject them directly into the image if you use ghost or imagex) and then modify your sysprep to run the commands. You launch commands in the RunSynchronous section of sysprep. You can either add/remove commands or just have one command that calls a batch file like setup.bat and modify your commands in that bat file.